To the Editor.—The contribution of low doses of ionizing radiation to breast cancer incidence remains uncertain because definitive studies have not been done. In their report, Dr Boice and colleagues1 claim the following: "Employment as a radiologic technologist... was not found to increase the risk of breast cancer. The contribution of prolonged exposure to relatively low doses of ionizing radiation to breast cancer risk was too small to be detectable at this time." If correct, this study would be strong evidence for the safety of low-dose exposure to ionizing radiation.Unfortunately, this study is so flawed that it provides no evidence about breast cancer induction after low-dose ionizing radiation. Boice and colleagues matched 5 control radiologic technologists to each breast cancer case for sex, date of birth, calendar year of certification, and length of time between certification and breast cancer diagnosis for cases or index date for controls.